Poly(amide-imide) copolymer, composition for preparing poly(amide-imide) copolymer, article including poly(amide-imide) copolymer, and display device including the article

ABSTRACT

A poly(amide-imide) copolymer that is a reaction product of a substituted or unsubstituted linear aliphatic diamine including two terminals, a diamine represented by Chemical Formula 1, a dicarbonyl compound represented by Chemical Formula 2, and a tetracarboxylic acid dianhydride represented by Chemical Formula 3:wherein, in Chemical Formulae 1 to 3, A, R3, R10, R12, R13, X, n7 and n8 are the same as defined in the specification.

CROSS-REFERENCE TO RELATED APPLICATION

This application claims priority to Korean Patent Application No.10-2017-0115218, filed on Sep. 8, 2017, and all the benefits accruingtherefrom under 35 U.S.C. § 119, the content of which is incorporatedherein in its entirety by reference.

BACKGROUND 1. Field

This disclosure relates to a poly(amide-imide) copolymer, a compositionfor preparing a poly(amide-imide) copolymer, an article including apoly(amide-imide) copolymer, and to a display device including thearticle.

2. Description of the Related Art

A flexible display, which is not restricted by time and place, that isthin and flexible like paper, ultra light, and consumes a small amountof electricity, has been increasingly in demand as a display forvisualizing various information and delivering it to the users. Theflexible display may be realized by using a flexible substrate, organicand inorganic materials for a low temperature process, flexibleelectronics, encapsulation, packaging, and the like.

A transparent plastic film for replacing a conventional window coverglass to be used in a flexible display must have high toughness andexcellent optical properties. Desired optical properties include highlight transmittance, low haze, low yellowness index, low YI differenceafter exposure to UV light, and the like.

There still remains a need for polymers having excellent optical andmechanical properties that could be used in transparent plastic films.

SUMMARY

An embodiment provides a poly(amide-imide) copolymer having improvedoptical and mechanical properties.

Another embodiment provides a composition for preparing apoly(amide-imide) copolymer.

Still another embodiment provides an article including apoly(amide-imide) copolymer.

Yet another embodiment provides a display device including an articleincluding the poly(amide-imide) copolymer.

According to an embodiment, provided is a poly(amide-imide) copolymerthat is a reaction product of a substituted or unsubstituted linearaliphatic diamine including two terminals, a diamine represented byChemical Formula 1, a dicarbonyl compound represented by ChemicalFormula 2, and a tetracarboxylic acid dianhydride represented byChemical Formula 3:

NH₂-A-NH₂  Chemical Formula 1

wherein in Chemical Formula 1,

A is a ring system including two or more C6 to C30 aromatic rings linkedby a single bond, wherein each of the two or more of the aromatic ringsis independently unsubstituted or substituted by an electron-withdrawinggroup;

wherein, in Chemical Formula 2,

R³ is a substituted or unsubstituted phenylene or a substituted orunsubstituted biphenylene group, and each X is an identical or adifferent halogen atom,

wherein, in Chemical Formula 3,

R¹⁰ is a single bond, —O—, —S—, —C(═O)—, —CH(OH)—, —C(═O)NH—, —S(═O)₂—,—Si(CH₃)₂—, —(CH₂)_(p)—, —(CF₂)_(q)—, —C(C_(n)H_(2n+1))₂—,—C(C_(n)F_(2n+1))₂—, —(CH₂)_(p)C(C_(n)H_(2n+1))₂(CH₂)_(q)—, or—(CH₂)_(p)C(C_(n)F_(2n+1))₂(CH₂)_(q)— wherein 1≤n≤10, 1≤p≤10, and1≤q≤10,

R¹² and R¹³ are each independently a halogen, a hydroxy group, asubstituted or unsubstituted C1 to C10 aliphatic organic group, asubstituted or unsubstituted C6 to C20 aromatic organic group, an alkoxygroup of formula —OR²⁰¹, wherein R²⁰¹ is a C1 to C10 aliphatic organicgroup, or a silyl group of formula —SiR²¹⁰R²¹¹R²¹², wherein R²¹⁰, R²¹¹,and R²¹² are each independently hydrogen or a C1 to C10 aliphaticorganic group,

n7 and n8 are each independently an integer ranging from 0 to 3.

The substituted or unsubstituted linear aliphatic diamine includes anamino group located at each end of the two terminals thereof, and may bea substituted or unsubstituted C1 to C30 saturated or unsaturated linearaliphatic diamine.

The substituted or unsubstituted linear aliphatic diamine includes anamino group located at each end of the two terminals thereof, and may bea substituted or unsubstituted C1 to C20 saturated linear aliphaticdiamine.

The substituted or unsubstituted linear aliphatic diamine may beselected from methylene diamine, ethylene diamine, 1,3-propane diamine,1,4-tetramethylene diamine, 1,5-pentamethylene diamine,1,6-hexamethylene diamine, 1,7-heptamethylene diamine, 1,8-octamethylenediamine, 1,9-nanomethylene diamine, 1,10-decamehtylene diamine,1,11-undecamethylene diamine, 1,12-dodecamethylene diamine, and acombination thereof.

The diamine represented by Chemical Formula 1 may have a ring systemincluding two C6 to C12 aromatic rings linked by a single bond, whereineach of the two C6 to C12 aromatic rings may be substituted by anelectron-withdrawing group selected from a halogen atom, a nitro group,a cyano group, a C1 or C2 haloalkyl group, a C2 to C6 alkanoyl group,and a C1 to C6 ester group.

The diamine represented by Chemical Formula 1 may include at least oneselected from the diamines represented by chemical formulae:

The diamine represented by Chemical Formula 1 may include the diaminerepresented by Chemical Formula A:

In Chemical Formula 2, R³ may be a phenylene group, and each X may beindependently Cl or Br.

The tetracarboxylic acid dianhydride represented by Chemical Formula 3may include at least one selected from 3,3′,4,4′-biphenyltetracarboxylic dianhydride (BPDA), 3,3′,4,4′-diphenylsulfonetetracarboxylic dianhydride (DSDA),4,4′-(hexafluoroisopropylidene)diphthalic anhydride (6FDA), and4,4′-oxydiphthalic anhydride (ODPA).

The tetracarboxylic acid dianhydride represented by Chemical Formula 3may include a combination of 3,3,4,4-biphenyl tetracarboxylicdianhydride (BPDA) and 4,4′-(hexafluoroisopropylidene)diphthalicanhydride (6FDA).

An amount of the substituted or unsubstituted linear aliphatic diaminemay be greater than 20 mole percent and less than 90 mole percent basedon the total amount of the substituted or unsubstituted linear aliphaticdiamine and the diamine represented by Chemical Formula 1.

A mole ratio of the dicarbonyl compound represented by Chemical Formula2 and the tetracarboxylic acid dianhydride represented by ChemicalFormula 3 may be 10 to 80:90 to 20.

According to an embodiment, provided is a composition for preparing apoly(amide-imide) copolymer including a substituted or unsubstitutedlinear aliphatic diamine, a compound represented by Chemical Formula 4,and a tetracarboxylic acid dianhydride represented by Chemical Formula3:

wherein, in Chemical Formula 4,

R³ is a substituted or unsubstituted phenylene or a substituted orunsubstituted biphenylene group,

n0 is a number greater than or equal to 0,

Ar¹ and Ar² are each independently represented by Chemical Formula 5:

wherein, in Chemical Formula 5,

R⁶ and R⁷ are each independently an electron withdrawing group selectedfrom —CF₃, —CCl₃, —CBr₃, —Cl₃, —NO₂, —CN, —C(═O)CH₃, and —CO₂C₂H₅,

R⁸ and R⁹ are each independently a halogen, a hydroxy group, asubstituted or unsubstituted C1 to C10 aliphatic organic group, asubstituted or unsubstituted C6 to C20 aromatic organic group, an alkoxygroup of formula —OR²⁰⁴, wherein R²⁰⁴ is a C1 to C10 aliphatic organicgroup, or a silyl group of formula —SiR²⁰⁵R²⁰⁶R²⁰⁷ wherein R²⁰⁵, R²⁰⁶,and R²⁰⁷ are each independently hydrogen or a C1 to C10 aliphaticorganic group,

n3 is an integer ranging from 1 to 4, n5 is an integer ranging from 0 to3, provided that n3+n5 is an integer ranging from 1 to 4, and

n4 is an integer ranging from 1 to 4, n6 is an integer ranging from 0 to3, provided that n4+n6 is an integer ranging from 1 to 4;

wherein, in Chemical Formula 3,

R¹⁰ is a single bond, —O—, —S—, —C(═O)—, —CH(OH)—, —C(═O)NH—, —S(═O)₂—,—Si(CH₃)₂—, —(CH₂)_(p)—, —(CF₂)_(q)—, —C(C_(n)H_(2n+1))₂—,—C(C_(n)F_(2n+1))₂—, —(CH₂)_(p)C(C_(n)H_(2n+1))₂(CH₂)_(q)—, or—(CH₂)_(p)C(C_(n)F_(2n+1))₂(CH₂)_(q)— wherein 1≤n≤10, 1≤p≤10, and1≤q≤10,

R¹² and R¹³ are each independently a halogen, a hydroxy group, asubstituted or unsubstituted C1 to C10 aliphatic organic group, asubstituted or unsubstituted C6 to C20 aromatic organic group, an alkoxygroup of formula —OR²⁰¹, wherein R²⁰¹ is a C1 to C10 aliphatic organicgroup, or a silyl group of formula —SiR²¹⁰R²¹¹R²¹², wherein R²¹⁰, R²¹¹,and R²¹² are each independently hydrogen or a C1 to C10 aliphaticorganic group, and

n7 and n8 are each independently an integer ranging from 0 to 3.

The composition may further include a diamine represented by ChemicalFormula 1:

NH₂-A-NH₂  Chemical Formula 1

wherein in Chemical Formula 1,

A is a ring system including two or more C6 to C30 aromatic rings linkedby a single bond, wherein each of the two or more aromatic rings isindependently unsubstituted or substituted by an electron-withdrawinggroup.

The substituted or unsubstituted linear aliphatic diamine comprises twoterminals, wherein the substituted or unsubstituted linear aliphaticdiamine includes an amino group located at each end of the two terminalsthereof, and wherein the substituted or unsubstituted linear aliphaticdiamine may be a substituted or unsubstituted C1 to C30 saturated orunsaturated linear aliphatic diamine.

The substituted or unsubstituted linear aliphatic diamine includes anamino group located at each end of the two terminals thereof, and may bea substituted or unsubstituted C1 to C20 saturated linear aliphaticdiamine.

The tetracarboxylic acid dianhydride represented by Chemical Formula 3may be a combination of the compound represented by Chemical Formula 3-1and the compound represented by Chemical Formula 3-2:

According to another embodiment, provided is an article including apoly(amide-imide) copolymer according to an embodiment.

The article may be a film, wherein the film may have a toughness ofgreater than or equal to 1,000 Joules×reverse cubic meters×10⁴(Joul·m⁻³·10⁴), and a refractive index of less than or equal to 1.68,when the film has a thickness of about 30 micrometers to about 100micrometers.

According to another embodiment, provided is a display device includingan article according to an embodiment.

Hereinafter, further embodiments will be described in detail.

DETAILED DESCRIPTION

This disclosure will be described more fully hereinafter. Thisdisclosure may, however, be embodied in many different forms and is notto be construed as limited to the exemplary embodiments set forthherein.

It will be understood that when an element is referred to as being “on”another element, it may be directly on the other element or interveningelements may be present therebetween. In contrast, when an element isreferred to as being “directly on” another element, there are nointervening elements present.

It will be understood that, although the terms first, second, third etc.may be used herein to describe various elements, components, regions,layers and/or sections, these elements, components, regions, layersand/or sections should not be limited by these terms. These terms areonly used to distinguish one element, component, region, layer orsection from another element, component, region, layer, or section.Thus, a first element, component, region, layer, or section discussedbelow could be termed a second element, component, region, layer, orsection without departing from the teachings of the present embodiments.

The terminology used herein is for the purpose of describing particularembodiments only and is not intended to be limiting. As used herein, thesingular forms “a,” “an” and “the” are intended to include the pluralforms as well, unless the context clearly indicates otherwise. The term“or” means “and/or.” As used herein, the term “and/or” includes any andall combinations of one or more of the associated listed items.Expressions such as “at least one of,” when preceding a list ofelements, modify the entire list of elements and do not modify theindividual elements of the list.

It will be further understood that the terms “comprises” and/or“comprising,” or “includes” and/or “including” when used in thisspecification, specify the presence of stated features, regions,integers, steps, operations, elements, and/or components, but do notpreclude the presence or addition of one or more other features,regions, integers, steps, operations, elements, components, and/orgroups thereof.

Unless otherwise defined, all terms (including technical and scientificterms) as used herein have the same meaning as commonly understood byone of ordinary skill in the art to which this general inventive conceptbelongs. It will be further understood that terms, such as those definedin commonly used dictionaries, should be interpreted as having a meaningthat is consistent with their meaning in the context of the relevant artand the present disclosure, and will not be interpreted in an idealizedor overly formal sense unless expressly so defined herein.

“About” or “approximately” as used herein is inclusive of the statedvalue and means within an acceptable range of deviation for theparticular value as determined by one of ordinary skill in the art,considering the measurement in question and the error associated withmeasurement of the particular quantity (i.e., the limitations of themeasurement system).

“Mixture” as used herein is inclusive of all types of combinations,including blends, alloys, solutions, and the like.

As used herein, when a specific definition is not otherwise provided,the term “substituted” refers to a group or compound substituted with atleast one substituent including a halogen (—F, —Br, —Cl, or —I), ahydroxy group, a nitro group, a cyano group, an amino group (—NH₂,—NH(R¹⁰⁰) or —N(R¹⁰¹)(R¹⁰²), wherein R¹⁰⁰, R¹⁰¹, and R¹⁰² are the sameor different, and are each independently a C1 to C10 alkyl group), anamidino group, a hydrazine group, a hydrazone group, a carboxyl group,an ester group, a ketone group, a substituted or unsubstituted alkylgroup, a substituted or unsubstituted alicyclic organic group, asubstituted or unsubstituted aryl group, a substituted or unsubstitutedalkenyl group, a substituted or unsubstituted alkynyl group, asubstituted or unsubstituted heteroaryl group, and a substituted orunsubstituted heterocyclic group, in place of at least one hydrogen of afunctional group, or the substituents may be linked to each other toprovide a ring.

As used herein, the term “alkyl group” refers to a straight or branchedchain saturated aliphatic hydrocarbon group having the specified numberof carbon atoms and having a valence of one. Non-limiting examples ofthe alkyl group are methyl, ethyl, and propyl.

As used herein, the term “alkoxy group” refers to “alkyl-O—”, whereinthe term “alkyl” has the same meaning as described above. Non-limitingexamples of the alkoxy group are methoxy, ethoxy, and propoxy.

As used herein, when a definition is not otherwise provided, the term“alkanoyl” represents “alkyl-C(═O)—”, wherein the term “alkyl” has thesame meaning as described above.

As used herein, the term “aryl group”, which is used alone or incombination, refers to an aromatic hydrocarbon group containing at leastone ring. Non-limiting examples of the aryl group are phenyl, naphthyl,and tetrahydronaphthyl.

As used herein, the term “alkylene” indicates a straight or branchedsaturated aliphatic hydrocarbon group having a valence of at least two,optionally substituted with one or more substituents where indicated,provided that the valence of the alkylene group is not exceeded.

As used herein, the term “cycloalkylene” indicates a saturated cyclichydrocarbon group having a valence of at least two, optionallysubstituted with one or more substituents where indicated, provided thatthe valence of the cycloalkylene group is not exceeded.

As used herein, when a definition is not otherwise provided, the term“arylene” indicates a divalent or higher valent group formed by theremoval of two or more hydrogen atoms from one or more rings of anarene, wherein the hydrogen atoms may be removed from the same ordifferent rings of the arene.

As used herein, when a specific definition is not otherwise provided,the term “alkyl group” refers to a C1 to C30 alkyl group, for example, aC1 to C15 alkyl group, the term “cycloalkyl group” refers to a C3 to C30cycloalkyl group, for example, a C3 to C18 cycloalkyl group, the term“alkoxy group” refer to a C1 to C30 alkoxy group, for example, a C1 toC18 alkoxy group, the term “ester group” refers to a C2 to C30 estergroup, for example, a C2 to C18 ester group, the term “ketone group”refers to a C3 to C30 ketone group, for example, a C3 to C18 ketonegroup, the term “aryl group” refers to a C6 to C30 aryl group, forexample, a C6 to C18 aryl group, the term “alkenyl group” refers to a C2to C30 alkenyl group, for example, a C2 to C18 alkenyl group, the term“alkynyl group” refers to a C2 to C30 alkynyl group, for example, a C2to C18 alkynyl group, the term “alkylene group” refers to a C1 to C30alkylene group, for example, a C1 to C18 alkylene group, and the term“arylene group” refers to a C6 to C30 arylene group, for example, a C6to C16 arylene group.

As used herein, when a specific definition is not otherwise provided,the term “aliphatic organic group” refers to a C1 to C30 alkyl group, aC2 to C30 alkenyl group, a C2 to C30 alkynyl group, a C1 to C30 alkylenegroup, a C2 to C30 alkenylene group, or a C2 to C30 alkynylene group,for example, a C1 to C15 alkyl group, a C2 to C15 alkenyl group, a C2 toC15 alkynyl group, a C1 to C15 alkylene group, a C2 to C15 alkenylenegroup, or a C2 to C15 alkynylene group, the term “alicyclic organicgroup” refers to a C3 to C30 cycloalkyl group, a C3 to C30 cycloalkenylgroup, a C3 to C30 cycloalkynyl group, a C3 to C30 cycloalkylene group,a C3 to C30 cycloalkenylene group, or a C3 to C30 cycloalkynylene group,for example, a C3 to C15 cycloalkyl group, a C3 to C15 cycloalkenylgroup, a C3 to C15 cycloalkynyl group, a C3 to C15 cycloalkylene group,a C3 to C15 cycloalkenylene group, or a C3 to C15 cycloalkynylene group.

As used herein when a definition is not otherwise provided, the term“aromatic organic group” refers to a C6 to C30 group including onearomatic ring, two or more aromatic rings fused together to provide acondensed ring system, or two or more moieties independently selectedfrom the foregoing (a single aromatic ring or a condensed ring system)linked through a single bond or through a functional group selected froma fluorenylene group, —O—, —S—, —C(═O)—, —CH(OH)—, —S(═O)₂—, —Si(CH₃)₂—,—(CH₂)_(p)—, wherein 1≤p≤10, —(CF₂)_(q)—, wherein 1≤q≤10, —C(CH₃)₂—,—C(CF₃)₂—, and —C(═O)NH—, for example, through —S(═O)₂—, for example aC6 to C30 aryl group or a C6 to C30 arylene group, for example, a C6 toC16 aryl group or a C6 to C16 arylene group such as phenylene. Anexample of an aromatic organic group is a fluorenylene group.

As used herein, when a specific definition is not otherwise provided,the term “heterocyclic group” refers to a C2 to C30 heterocycloalkylgroup, a C2 to C30 heterocycloalkylene group, a C2 to C30heterocycloalkenyl group, a C2 to C30 heterocycloalkenylene group, a C2to C30 heterocycloalkynyl group, a C2 to C30 heterocycloalkynylenegroup, a C2 to C30 heteroaryl group, or a C2 to C30 heteroarylene groupincluding 1 to 3 heteroatoms selected from O, S, N, P, Si, and acombination thereof in one ring, for example, a C2 to C15heterocycloalkyl group, a C2 to C15 heterocycloalkylene group, a C2 toC15 heterocycloalkenyl group, a C2 to C15 heterocycloalkenylene group, aC2 to C15 heterocycloalkynyl group, a C2 to C15 heterocycloalkynylenegroup, a C2 to C15 heteroaryl group, or a C2 to C15 heteroarylene groupincluding 1 to 3 heteroatoms selected from O, S, N, P, Si, and acombination thereof, in one ring.

When a group containing a specified number of carbon atoms issubstituted with any of the groups listed in the preceding paragraph,the number of carbon atoms in the resulting “substituted” group isdefined as the sum of the carbon atoms contained in the original(unsubstituted) group and the carbon atoms (if any) contained in thesubstituent. For example, when the term “substituted C1 to C30 alkyl”refers to a C1 to C30 alkyl group substituted with C6 to C30 aryl group,the total number of carbon atoms in the resulting aryl substituted alkylgroup is C7 to C60.

As used herein, when a definition is not otherwise provided,“combination” commonly refers to mixing or copolymerization.

As used herein, when a definition is not otherwise provided, “polyimide”may refer to not only “polyimide” itself which is an imidization productof a polyamic acid, but also “polyamic acid” or a combination of the“polyimide” itself and “polyamic acid”. Further, the terms “polyimide”and “polyamic acid” may be understood as the same material.

In addition, in the specification, the mark “*” may refer to a point ofattachment to another atom.

Research efforts towards converting mobile devices, such as, a mobilephone or a tablet personal computer, and the like, to light, flexible,and bendable devices are currently ongoing. In this regard, a flexibleand transparent window film for a display device having high hardnessfor replacing a rigid glass placed on top of the mobile devices isdesired.

To be used as a window film, good optical and mechanical properties aredesired. Desired optical properties include high light transmittance,low yellowness index (YI), low YI difference after exposure to UV light,low haze, low refractive index (low reflection index), and the like.Mechanical properties, such as hardness, may be supplemented with a hardcoating layer, but a base film having high toughness may ensure that afinal film has high mechanical properties.

A polyimide or poly(amide-imide) copolymer has excellent mechanical,thermal, and optical properties, and thus, is widely used as a plasticsubstrate for a display device, such as an organic light emitting diode(OLED), liquid crystal display (LCD), and the like. In order to usepolyimide or poly(amide-imide) film as a window film for a flexibledisplay device, however, further improved mechanical and opticalproperties, such as, high hardness (or modulus), toughness, high lighttransmittance, low yellowness index, low refractive index, and the like,are desired. It is difficult, however, to improve both mechanical andoptical properties of the film at the same time, as the two properties,especially, tensile modulus and yellowness index of a polyimide orpoly(amide-imide) film are in a trade-off relationship with regard toeach other.

Meanwhile, in an effort to improve mechanical properties of apoly(amide-imide) copolymer film, researchers prepared apoly(amide-imide) copolymer by increasing the amount of an amidestructural unit, or by including a dianhydride having a more rigidstructure. However, the tensile modulus of such poly(amide-imide)copolymer is barely improved, while optical properties, such as YI, aredeteriorated. In addition, refractive index of a film prepared from thepoly(amide-imide) copolymer may increase to boost reflection index, orthe toughness of the film may reduce.

The inventors of the subject matter of the present application havestudied to develop a poly(amide-imide) copolymer having good opticalproperties, as well as improved toughness, and a composition forpreparing the poly(amide-imide). As a result, they have found apoly(amide-imide) copolymer prepared by copolymerizing an aromatictetracarboxylic dianhydride, an aromatic diamine, and an aromaticdicarbonyl compound, as monomers conventionally used for preparing apoly(amide-imide), and an additional substituted or unsubstituted linearaliphatic diamine, exhibits greatly improved toughness, as well asexcellent optical properties. Moreover, the prepared poly(amide-imide)has a reduced glass transition temperature (T_(g)) as the polymerbackbone has increased flexibility and segmental motion derived from thelinear aliphatic diamine, and thus, may be made to a film at a lowertemperature. This may lead to the cost reduction of fabricating a film.Further, as T_(g) becomes lower, the amount of solvent remained in afinal article, such as, for example, a film, reduces.

Accordingly, an embodiment provides a poly(amide-imide) copolymer thatis a reaction product of a substituted or unsubstituted linear aliphaticdiamine, a diamine represented by Chemical Formula 1, a dicarbonylcompound represented by Chemical Formula 2, and a tetracarboxylic aciddianhydride represented by Chemical Formula 3:

NH₂-A-NH₂  Chemical Formula 1

wherein in Chemical Formula 1,

A is a ring system including two or more C6 to C30 aromatic rings linkedby a single bond, wherein each of the two or more aromatic rings isindependently unsubstituted or substituted by an electron-withdrawinggroup,

wherein, in Chemical Formula 2,

R³ is a substituted or unsubstituted phenylene or a substituted orunsubstituted biphenylene group, and each X is an identical or adifferent halogen atom.

wherein, in Chemical Formula 3,

R¹⁰ is a single bond, —O—, —S—, —C(═O)—, —CH(OH)—, —C(═O)NH—, —S(═O)₂—,—Si(CH₃)₂—, —(CH₂)_(p)—, —(CF₂)_(q)—, —C(C_(n)H_(2n+1))₂—,—C(C_(n)F_(2n+1))₂—, —(CH₂)_(p)C(C_(n)H_(2n+1))₂(CH₂)_(q)—, or—(CH₂)_(p)C(C_(n)F_(2n+1))₂(CH₂)_(q)— wherein 1≤n≤10, 1≤p≤10, and1≤q≤10,

R¹² and R¹³ are each independently a halogen, a hydroxy group, asubstituted or unsubstituted C1 to C10 aliphatic organic group, asubstituted or unsubstituted C6 to C20 aromatic organic group, an alkoxygroup of formula —OR²⁰¹, wherein R²⁰¹ is a C1 to C10 aliphatic organicgroup, or a silyl group of formula —SiR²¹⁰R²¹¹R²¹², wherein R²¹⁰, R²¹¹,and R²¹² are each independently hydrogen or a C1 to C10 aliphaticorganic group,

n7 and n8 are each independently an integer ranging from 0 to 3.

The substituted or unsubstituted linear aliphatic diamine includes anamino group located at each end of the two terminals thereof, and may bea substituted or unsubstituted C1 to C30 saturated or unsaturated linearaliphatic diamine. For example, the substituted or unsubstituted linearaliphatic diamine includes an amino group located at each end of the twoterminals thereof, and the linear aliphatic diamine may be a substitutedor unsubstituted C1 to C30 saturated linear aliphatic diamine, or asubstituted or unsubstituted C2 to C30 unsaturated linear aliphaticdiamine having one or more carbon-carbon double bond or carbon-carbontriple bond.

When the substituted or unsubstituted linear aliphatic diamine is asubstituted linear aliphatic diamine, the substitution indicates thatone or more hydrogen bound to a carbon atom is substituted by anotheratom or a group selected from, for example, deuterium, a halogen,hydroxyl group, a cyano group, a nitro group, a haloalkyl group, acarboxyl group, an epoxy group, a glicydoxypropyl group, and the like,but is not limited thereto, and may be substituted by any atom or groupthat does not adversely affect the optical or mechanical properties ofthe poly(amide-imide) copolymer prepared therefrom.

In an exemplary embodiment, the substituted or unsubstituted linearaliphatic diamine includes an amino group located at each end of the twoterminals thereof, and may be an unsubstituted C1 to C30 saturatedlinear aliphatic diamine, for example, an unsubstituted C1 to C20saturated linear aliphatic diamine, for example, an unsubstituted C1 toC16 saturated linear aliphatic diamine, for example, and anunsubstituted C1 to C12 saturated linear aliphatic diamine, and forexample, may be selected from methylene diamine, ethylene diamine,1,3-propane diamine, 1,4-tetramethylene diamine, 1,5-pentamethylenediamine, 1,6-hexamethylene diamine, 1,7-heptamethylene diamine,1,8-octamethylene diamine, 1,9-nanomethylene diamine, 1,10-decamehtylenediamine, 1,11-undecamethylene diamine, 1,12-dodecamethylene diamine, ora combination thereof, but is not limited thereto.

Meanwhile, although the linear aliphatic diamines exemplified above arethose having a straight chain, the linear aliphatic diamine is notlimited thereto, but may also include those linear but having a branchfrom a carbon atom in the straight chain.

The diamine represented by Chemical Formula 1 may have a ring systemincluding two C6 to C12 aromatic rings linked by a single bond, whereineach of the two C6 to C12 aromatic rings may independently besubstituted by an electron-withdrawing group selected from an halogenatom, a nitro group, a cyano group, a C1 or C2 haloalkyl group, a C2 toC6 alkanoyl group, or a C1 to C6 ester group.

In an exemplary embodiment, the electron-withdrawing group substitutedto each of the aromatic rings of the diamine represented by ChemicalFormula 1 may be selected from an halogen atom, —CF₃, —CCl₃, —CBr₃, or—C₃.

The diamine represented by Chemical Formula 1 may include at least oneselected from the diamines represented by the following chemicalformulae:

The diamine represented by Chemical Formula 1 may include a diaminerepresented by Chemical Formula A, i.e.,2,2′-bis(trifluoromethyl)benzidine (TFDB):

In Chemical Formula 2, R³ may be a phenylene group, and each X may beindependently Cl or Br.

In an exemplary embodiment, the dicarbonyl compound represented byChemical Formula 3 may be terephthaloyl dichloride (TPCI).

The tetracarboxylic acid dianhydride represented by Chemical Formula 3may include at least one selected from 3,3′,4,4′-biphenyltetracarboxylic dianhydride (BPDA), 3,3′,4,4′-diphenylsulfonetetracarboxylic dianhydride (DSDA),4,4′-(hexafluoroisopropylidene)diphthalic anhydride (6FDA), and4,4′-oxydiphthalic anhydride (ODPA), and is not limited thereto.

In an exemplary embodiment, the tetracarboxylic acid dianhydriderepresented by Chemical Formula 3 may be a combination of the compoundrepresented by Chemical Formula 3 wherein R¹⁰ is a single bond, and bothn7 and n8 are 0, that is, for example, 3,3′,4,4′-biphenyltetracarboxylic dianhydride (BPDA), and the compound represented byChemical Formula 3 wherein R¹⁰ is —C(C_(n)F_(2n+1))₂— wherein 1≤n≤10,and both n7 and n8 are 0, that is, for example,4,4′-(hexafluoroisopropylidene)diphthalic anhydride (6FDA).

At least one of the substituted or unsubstituted linear aliphaticdiamine and the diamine represented by Chemical Formula 1 may react witha dicarbonyl compound represented by Chemical Formula 2 to provide anamide structural unit in a poly(amide-imide) copolymer, and at least oneof the substituted or unsubstituted linear aliphatic diamine and thediamine represented by Chemical Formula 1 may react with atetracarboxylic acid dianhydride represented by Chemical Formula 3 toprovide an imide structural unit in a poly(amide-imide) copolymer.

A conventional method for preparing a poly(amide-imide) copolymer mayinclude preparing an amide structural unit by reacting a dicarbonylcompound represented by Chemical Formula 2, such as, for example, adicarbonyl chloride, with a diamine, such as, for example, at least oneof the substituted or unsubstituted linear aliphatic diamine and thediamine represented by Chemical Formula 1, to prepare an amidestructural unit, and further adding and reacting an additional diamine,such as, for example, at least one of the substituted or unsubstitutedlinear aliphatic diamine and the diamine represented by Chemical Formula1, with a tetracarboxylic acid dianhydride, for example, atetracarboxylic acid dianhydride represented by Chemical Formula 3, toprepare an amic acid structural unit, as well as to link the preparedamide structural unit and the amic acid structural unit to provide apoly(amide-amic acid) copolymer. Thus prepared poly(amide-amic acid)copolymer may be partially or completely imidized by chemical and/orthermal imidization reaction. Then, the obtained poly(amide-amic acidand/or imide) copolymer may be precipitated, filtered, and/or furtherheat-treated to provide a final poly(amide-imide) copolymer. This methodis well known to persons skilled in the art to which the presentinventive concept pertains.

An amide structural unit prepared by reacting a substituted orunsubstituted linear aliphatic diamine, for example, an unsubstitutedlinear aliphatic saturated diamine, and a dicarbonyl compoundrepresented by Chemical Formula 2 may be represented by Chemical Formula7, and an amide structural unit prepared by reacting a diaminerepresented by Chemical Formula 1 and a dicarbonyl compound representedby Chemical Formula 2 may be represented by Chemical Formula 8:

wherein in Chemical Formula 7,

R³ is the same as defined for Chemical Formula 3, and

n is an integer of greater than or equal to 1, for example, an integerranging from 1 to 30.

wherein in Chemical Formula 8,

R³ is the same as defined for Chemical Formula 3, and A is the same asdefined for Chemical Formula 1.

Meanwhile, an imide structural unit prepared by reacting a substitutedor unsubstituted linear aliphatic diamine, for example, an unsubstitutedlinear aliphatic saturated diamine, and a tetracarboxylic aciddianhydride represented by Chemical Formula 3 may be represented byChemical Formula 9, and an imide structural unit prepared by reacting adiamine represented by Chemical Formula 1 and a tetracarboxylic aciddianhydride represented by Chemical Formula 3 may be represented byChemical Formula 10:

wherein in Chemical Formula 9,

each of R¹⁰, R¹², R¹³, n7 and n8 are the same as defined for ChemicalFormula 3, and

n is an integer of greater than or equal to 1, for example, an integerranging from 1 to 30;

wherein in Chemical Formula 10,

A is the same as defined for Chemical Formula 1, and

R¹⁰, R¹², R¹³, n7 and n8 are the same as defined for Chemical Formula 3.

Therefore, a poly(amide-imide) copolymer according to an embodiment mayinclude an amide structural unit represented by at least one of ChemicalFormula 7 and Chemical Formula 8, and an imide structural unitrepresented by at least one of Chemical Formula 9 and Chemical Formula10, provided that the poly(amide-imide) copolymer is not consisting ofan amide structural unit represented by Chemical Formula 7 and an imidestructural unit represented by Chemical Formula 9, or of an amidestructural unit represented by Chemical Formula 8 and an imidestructural unit represented by Chemical Formula 10.

The substituted or unsubstituted linear aliphatic diamine may beincluded in an amount of less than 90 mole percent (mole %), forexample, greater than 20 mole % and less than 90 mole %, for example,greater than or equal to about 25 mole % and less than or equal to about85 mole %, and for example, greater than or equal to about 30 mole % andless than or equal to about 80 mole %, based on the total amount of thesubstituted or unsubstituted linear aliphatic diamine and the diaminerepresented by Chemical Formula 1.

By including the substituted or unsubstituted linear aliphatic diamine,along with the diamine represented by Chemical Formula 1, in the aboverange, and reacting them with a dicarbonyl compound represented byChemical Formula 2 and a tetracarboxylic acid dianhydride represented byChemical Formula 3, thus prepared poly(amide-imide) copolymer may havegood mechanical properties, such as, for example, a toughness of greaterthan or equal to about 1,000 Joul·m⁻³·10⁴, a low T_(g), such as, forexample, less than 270° C., as well as excellent optical properties.

If the amount of the substituted or unsubstituted linear aliphaticdiamine is less than or equal to 20 mole % based on the total amount ofthe diamines, improvement in toughness may be hardly expected, while ifthe amount is greater than or equal to 90 mole % based on the totalamount of the diamines, the tensile modulus may substantially bedeteriorated.

The dicarbonyl compound represented by Chemical Formula 2 and thetetracarboxylic acid dianhydride represented by Chemical Formula 3 maybe included in a mole ratio of 10 to 80:90 to 20, for example, 10 to70:90 to 30, for example, 10 to 60:90 to 40, for example, 10 to 50:90 to50, for example, 10 to 40:90 to 60, and for example, 10 to 30:90 to 70.

By including the dicarbonyl compound represented by Chemical Formula 2and tetracarboxylic acid dianhydride represented by Chemical Formula 3at a mole ratio of the above, the prepared poly(amide-imide) copolymermay have improved mechanical properties, such as, for example, animproved toughness, while maintaining excellent optical properties, suchas, for example, a high transmittance, a low Yellowness Index (YI), asmall color change after exposing to Ultra Violet (UV) light, a lowhaze, and the like. For example, the poly(amide-imide) copolymeraccording to an embodiment may have a transmittance of about greaterthan or equal to about 89% at a wavelength range of 350 nanometers to750 nanometers, YI of less than 2.0, less than 1.1 of YI increase afterexposure to an ultraviolet (UV) lamp of a UVB wavelength region for 72hours, and a toughness of greater than or equal to 1,000 Joul·m⁻³·10⁴.Further, the poly(amide-imide) copolymer may have a low T_(g) of lessthan 270° C.

The tetracarboxylic acid dianhydride represented by Chemical Formula 3may be a combination of the compound represented by Chemical Formula 3wherein R¹⁰ is a single bond, and both n7 and n8 are 0, and the compoundrepresented by Chemical Formula 3 wherein R¹⁰ is —C(C_(n)F_(2n+1))₂—wherein 1≤n≤10, and both n7 and n8 are 0, in a mole ratio of 1:5 to 10,for example, 1:5 to 9, and for example, 1:6 to 8. In an exemplaryembodiment, the tetracarboxylic acid dianhydride represented by ChemicalFormula 3 may be a combination of 3,3′,4,4′-biphenyl tetracarboxylicdianhydride (BPDA) and 4,4′-(hexafluoroisopropylidene)diphthalicanhydride (6FDA), and in this case, by including BPDA and 6FDA in theabove ratio, the prepared poly(amide-imide) copolymer may have goodoptical properties, as well as improved mechanical properties.

When R¹⁰ is a single bond in the tetracarboxylic acid dianhydriderepresented by Chemical Formula 3, the tetracarboxylic acid dianhydridehas much more rigid structure than those having different groups as saidR¹⁰. It has been known that as the amount of the tetracarboxylic aciddianhydride having rigid structure increases, mechanical properties ofthe prepared poly(amide-imide) copolymer increases. However, althoughthe poly(amide-imide) copolymer according to an embodiment is preparedfrom a reactant wherein the amount of the tetracarboxylic aciddianhydride represented by Chemical Formula 3 having R¹⁰ which is not asingle bond is greater than that having R¹⁰ which is a single bond, thepoly(amide-imide) copolymer has improved mechanical properties, such as,for example, a high toughness of greater than or equal to about 1,000Joul·m⁻³·10⁴, while maintaining good optical properties, such as, forexample, a high light transmittance, for example, greater than or equalto about 89% in a wavelength range of 350 nm to 750 nm, and a YI of lessthan or equal to 2.0. Without being bound to a specific theory, it isunderstood that these results may derive from the improved flexibilityof the poly(amide-imide) copolymer according to an embodiment preparedby polymerizing a composition including a substituted or unsubstitutedlinear aliphatic diamine.

Accordingly, the poly(amide-imide) copolymer according to an embodimenthaving excellent optical and mechanical properties may be advantageousfor a use in a display device, such as, for example, as a window filmfor a flexible display device.

Another embodiment provides a composition for preparing apoly(amide-imide) copolymer including a substituted or unsubstitutedlinear aliphatic diamine, a compound represented by Chemical Formula 4,and a tetracarboxylic acid dianhydride represented by Chemical Formula3:

wherein, in Chemical Formula 4,

R³ is a substituted or unsubstituted phenylene or a substituted orunsubstituted biphenylene group,

n0 is a number greater than or equal to 0,

Ar¹ and Ar² are each independently represented by Chemical Formula 5:

wherein, in Chemical Formula 5,

R⁶ and R⁷ are each independently an electron withdrawing group selectedfrom —CF₃, —CCl₃, —CBr₃, —Cl₃, —NO₂, —CN, —C(═O)CH₃, and —CO₂C₂H₅,

R⁸ and R⁹ are each independently a halogen, a hydroxy group, asubstituted or unsubstituted C1 to C10 aliphatic organic group, asubstituted or unsubstituted C6 to C20 aromatic organic group, an alkoxygroup of formula —OR²⁰⁴, wherein R²⁰⁴ is a C1 to C10 aliphatic organicgroup, or a silyl group of formula —SiR²⁰⁵R²⁰⁶R²⁰⁷ wherein R²⁰⁵, R²⁰⁶,and R²⁰⁷ are each independently hydrogen or a C1 to C10 aliphaticorganic group,

n3 is an integer ranging from 1 to 4, n5 is an integer ranging from 0 to3, provided that n3+n5 is an integer ranging from 1 to 4, and

n4 is an integer ranging from 1 to 4, n6 is an integer ranging from 0 to3, provided that n4+n6 is an integer ranging from 1 to 4;

wherein, in Chemical Formula 3,

R¹⁰ is a single bond, —O—, —S—, —C(═O)—, —CH(OH)—, —C(═O)NH—, —S(═O)₂—,—Si(CH₃)₂—, —(CH₂)_(p)—, —(CF₂)_(q)—, —C(C_(n)H_(2n+1))₂—,—C(C_(n)F_(2n+1))₂—, —(CH₂)_(p)C(C_(n)H_(2n+1))₂(CH₂)_(q)—, or—(CH₂)_(p)C(C_(n)F_(2n+1))₂(CH₂)_(q)— wherein 1≤n≤10, 1≤p≤10, and1≤q≤10,

R¹² and R¹³ are each independently a halogen, a hydroxy group, asubstituted or unsubstituted C1 to C10 aliphatic organic group, asubstituted or unsubstituted C6 to C20 aromatic organic group, an alkoxygroup of formula —OR²⁰¹, wherein R²⁰¹ is a C1 to C10 aliphatic organicgroup, or a silyl group of formula —SiR²¹⁰R²¹¹R²¹², wherein R²¹⁰, R²¹¹,and R²¹² are each independently hydrogen or a C1 to C10 aliphaticorganic group, and

n7 and n8 are each independently an integer ranging from 0 to 3.

R³ of Chemical Formula 3 may be an unsubstituted phenylene group, bothR⁶ and R⁷ may be —CF₃, both n3 and n4 may be 1, and both n5 and n6 maybe 0 (zero).

As described above, in a conventional method for preparing apoly(amide-imide) copolymer, an amide structural unit may first beprepared by a reaction of a dicarbonyl compound and a diamine, and thenan additional diamine and a dianhydride compound are added to thereactor to prepare an amic acid structural unit, as well as apoly(amide-imide) copolymer by linking the amide structural unit and theamic acid structural unit. Meanwhile, in the process of preparing theamide structural unit, there is a problem that a by-product, such as,halogenated hydrogen (HX: ‘H’ indicates hydrogen, and ‘X’ indicateshalogen), for example, hydrogen chloride (HCl), is produced. Thehydrogen chloride by-product causes corrosion of an element of anapparatus, and thus, should necessarily be removed by a precipitationprocess. In order to remove the by-product, an HX scavenger, such as atertiary amine, may be added to the reactor, whereby a salt of HX isproduced (please see Reaction Scheme 1 below). If the produced salt ofHX is not removed and a film is produced therefrom, seriousdeterioration of optical properties of the produced film occurs.Therefore, a precipitation process to remove the salt of HX is requiredin the conventional method for preparing poly(amide-imide) copolymer.The precipitation process increases total process time and cost, whilereducing the yield of the final poly(amide-imide) copolymer producedtherefrom.

In addition to using the conventional method including the precipitationprocess as described above, it is also possible to prepare apoly(amide-imide) copolymer according to an embodiment by first reactinga diamine and a dicarbonyl compound to prepare an amide structuralunit-containing oligomer having amino groups located at both endsthereof (hereinafter, referred to as “an amide structuralunit-containing oligomer”), and then reacting the prepared amidestructural unit-containing oligomer as a diamine monomer with atetracarboxylic acid dianhydride to provide a poly(amide-imide)copolymer. According to the new method for preparing a poly(amide-imide)copolymer, the precipitation process for removing the HX salt may beomitted, and thus, not only the total process time and cost may bereduced, but also the yield of the final poly(amide-imide) copolymer mayincrease. Further, it is also possible to obtain a poly(amide-imide)copolymer including a higher amount of an amide structural unit thanthose prepared by using the conventional method, and thus, an articleprepared from the poly(amide-imide) copolymer, for example, a film, mayhave further improved mechanical properties, while maintaining goodoptical properties.

Accordingly, another embodiment provides a composition for preparing apoly(amide-imide) copolymer including an amide structuralunit-containing oligomer represented by Chemical Formula 4 as a diaminemonomer, which may be prepared by reacting a diamine and a dicarbonylcompound, a tetracarboxylic acid dianhydride represented by ChemicalFormula 3 for reacting with the oligomer to provide an imide structuralunit, and as an additional diamine, a substituted or unsubstitutedlinear aliphatic diamine for reacting with the tetracarboxylic aciddianhydride represented by Chemical Formula 3 to provide an imidestructural unit.

The compound represented by Chemical Formula 4 may be prepared byreacting a dicarbonyl compound represented by Chemical Formula 2 inwhich R³ is a substituted or unsubstituted phenylene group or asubstituted or unsubstituted biphenylene group, and one or twodiamine(s) represented by Chemical Formula 1 in which A is representedby Chemical Formula 5, wherein the diamine represented by ChemicalFormula 1 may be added in a greater amount than the dicarbonyl compoundrepresented by Chemical Formula 2 to provide an oligomer having aminogroups at both ends thereof. In this case, there may be a remainingdiamine that does not react with the dicarbonyl compound, which may alsobe represented by Chemical Formula 4, wherein n0 is 0 (zero).Accordingly, the diamine represented by Chemical Formula 4 wherein n0 is0 may also be reacted with a tetracarboxylic acid dianhydriderepresented by Chemical Formula 3 along with the compound represented byChemical Formula 4 wherein n0 is greater than or equal to 1 to preparean imide structural unit.

In an embodiment, the composition may further include a diaminerepresented by Chemical Formula 1:

NH₂-A-NH₂  Chemical Formula 1

wherein in Chemical Formula 1,

A is a ring system including two or more C6 to C30 aromatic rings linkedby a single bond, wherein each of the two or more aromatic rings isindependently unsubstituted or substituted by an electron-withdrawinggroup.

In an exemplary embodiment, the diamine represented by Chemical Formula1 may have a ring system including two C6 to C12 aromatic rings linkedby a single bond, wherein each of the two C6 to C12 aromatic rings mayindependently be substituted by an electron-withdrawing group selectedfrom an halogen atom, a nitro group, a cyano group, a C1 or C2 haloalkylgroup, a C2 to C6 alkanoyl group, or a C1 to C6 ester group.

In an exemplary embodiment, the diamine represented by Chemical Formula1 may include at least one selected from the diamines represented by thefollowing chemical formulae:

The diamine represented by Chemical Formula 1 may include a diaminerepresented by Chemical Formula A, i.e.,2,2′-bis(trifluoromethyl)benzidine (TFDB):

The tetracarboxylic acid dianhydride represented by Chemical Formula 3may be a combination of the compound represented by Chemical Formula 3-1and the compound represented by Chemical Formula 3-2, but is not limitedthereto:

The compound represented by Chemical Formula 3-1 may be 6FDA, thecompound represented by Chemical Formula 3-2 may be at least one ofs-BPDA, a-BPDA, and i-BPDA, and in an exemplary embodiment, the compoundrepresented by Chemical Formula 3-2 may be s-BPDA.

In an exemplary embodiment, an amount of the substituted orunsubstituted linear aliphatic diamine may be less than 90 mole %, forexample, greater than 20 mole % and less than 90 mole %, for example,greater than or equal to about 25 mole % and less than or equal to about85 mole %, and for example, greater than or equal to about 30 mole % andless than or equal to about 80 mole %, based on the total mole number ofthe substituted or unsubstituted linear aliphatic diamine and any otherdiamines required to prepare the poly(amide-imide) copolymer, which alsoinclude the diamine needed to prepare the compound represented byChemical Formula 4.

Explanations for the substituted or unsubstituted linear aliphaticdiamine, the diamine represented by Chemical Formula 1, the dicarbonylcompound represented by Chemical Formula 2, and the tetracarboxylic aciddianhydride represented by Chemical Formula 3 are the same as thosedescribed above for the poly(amide-imide) copolymer according to anembodiment, and thus, a more detailed explanation for the compounds areomitted here.

After preparing a poly(amide-imide) copolymer from the composition, anarticle may be formed from the poly(amide-imide) copolymer through adry-wet method, a dry method, or a wet method, but is not limitedthereto. When the article is a film, it may be manufactured using asolution including the composition through the dry-wet method, wherein alayer is formed by extruding the solution of the composition from amouth piece on a supporter, such as drum or an endless belt, drying thelayer by evaporating the solvent from the layer until the layer has aself-maintenance property. The drying may be performed by heating, forexample, from about 25° C. to about 150° C., within about 1 hour orless. Then, the dried layer may be heated from the room temperature toabout 250° C. or to about 300° C. at a heating rate of about 10° C. perminute, and then be allowed to stand at the heated temperature for about5 minutes to about 30 minutes to obtain a polyimide-based film.

When the surface of the drum and/or the endless belt used for the dryingprocess becomes flat, a layer with a flat surface is formed. The layerobtained after the drying process is delaminated from the supporter, andsubjected to a wet process, desalted, and/or desolventized. Themanufacturing of the film is completed after the layer is elongated,dried, and/or heat treated. The heat treatment may be performed at about200° C. to about 500° C., for example, at about 250° C. to about 400°C., for several seconds to several minutes. After the heat treatment,the layer may be cooled slowly, for example, at a cooling rate of lessthan or equal to about 50° C. per minute.

The layer may be formed as a single layer or multiple layers.

When prepared as a film, the film may have a yellowness index (YI) ofless than or equal to 2.1 at a thickness of about 35 micrometers (μm) toabout 100 μm according to an ASTM D1925 method, and a lighttransmittance of greater than or equal to 89% in a wavelength range of350 nm to 750 nm. Further, the yellowness difference (ΔYI) before andafter exposure to UVB lamp (greater than or equal to 200 millijoules persquare centimeter, mJ/cm²) for 72 hours may be less than 1.1, forexample, less than or equal to 0.95, and a refractive index may be lessthan or equal to 1.68, which prove very good optical properties.Further, toughness of the film may be greater than or equal to 1,000Joulm·⁻³·10⁴, which proves good mechanical properties.

That is, the article may maintain excellent optical properties of apoly(amide-imide) copolymer, such as, for example, a low YI and highlight transmittance, while having an improved and high toughness, andthus, may be advantageous for a use as a window film for a flexibledisplay device.

Hereafter, the technology of this disclosure is described in detail withreference to examples. The following examples and comparative examplesare not restrictive but are illustrative only.

EXAMPLES Synthesis Example 1: Preparation of an Oligomer Containing 70Mole % of an Amide Structural Unit as a Diamine Monomer

An amide structural unit-containing oligomer, as a diamine monomer, isprepared by reacting TPCI and 2,2′-bis(trifluoromethyl)benzidine (TFDB),in accordance with Reaction Scheme 2:

That is, 1 mole equivalent (0.122 mole, 39.2 grams) of2,2′-bis(trifluoromethyl)benzidine (TFDB) and 2.8 mole equivalent (0.343mole, 27.11 grams) of pyridine are dissolved in 700 g of N,N-dimethylacetamide (DMAc) as a solvent in a round-bottomed flask, and 50milliliters (mL) of DMAc is further added to the flask to dissolve theremaining TFDB. Then, 0.7 mole equivalent (0.086 mole, 17.4 g) ofterephthaloyl chloride (TPCI) is divided into 4 portions, which areindividually added, each portion at a time, to be mixed with the TFDBsolution. The mixture is then vigorously stirred and reacted for 15minutes at room temperature.

The resultant solution is further stirred under a nitrogen atmospherefor 2 hours, and then added to 7 liters of water containing 350 g ofNaCl. The resulting mixture is stirred for 10 minutes. Subsequently, asolid produced therein is filtered, re-suspended twice by using 5 liters(L) of deionized water, and then re-filtered. The water remaining in thefinal product on the filter is removed to the extent possible bythoroughly pressing the filtered precipitate on a filter. Theprecipitate is then dried at 90° C. under vacuum for 48 hours, to obtainan amide structural unit-containing oligomer represented in ReactionScheme 2, as a diamine monomer, as a final product. The preparedoligomer containing 70 mol % of amide structural unit has a numberaverage molecular weight of about 997 grams per mole (gram/mole).

Examples and Comparative Example: Preparation of Poly(Amide-Imide)Copolymer Films Example 1

168 grams of N,N-dimethyl acetamide (DMAc) as a solvent is charged intoa 4-neck double-walled 250 mL reactor equipped with a mechanical stirrerand a nitrogen inlet, while passing nitrogen gas through, and thetemperature is set to 25° C. Then, 17.327 grams of the 70 mol % of amidestructural unit-containing oligomer prepared in Synthesis Example 1,8.171 g of 2,2′-bis(trifluoromethyl)benzidine (TFDB), and 3.271 g ofhexamethylene diamine (HMDA) are added thereto and dissolved, and thetemperature is set to 25° C. Then, 3.231 grams of3,3′,4,4′-biphenyltetracarboxylic dianhydride (BPDA), and 24.336 gramsof 4,4′-(hexafluoroisopropylidene)diphthalic anhydride (6FDA) are addedthereto, and the mixture is stirred for 48 hours. Then, 5.20 grams ofpyridine and 20.14 grams of acetic anhydride are added thereto, and themixture is stirred for 24 hours to obtain a poly(amic acid-amide)copolymer solution, of which the solid content is 11.2 weight %.

After cooling the poly(amic acid-amide) solution to a temperature of 25°C., the solution is casted on a glass substrate, and dried for 40minutes on a hot plate at a temperature of 100° C. Then, the film isseparated from the glass substrate and introduced into a conventionoven, wherein the temperature is increased from the room temperature to200° C., at a heating rate of 3° C. per minutes, maintained at 200° C.for about 20 minutes, and slowly cooled to room temperature to obtain apoly(amide-imide) copolymer film.

Example 2

136 grams of N,N-dimethyl acetamide (DMAc) as a solvent is charged intoa 4-neck double-walled 250 mL reactor equipped with a mechanical stirrerand a nitrogen inlet, while passing nitrogen gas through, and thetemperature is set to 25° C. Then, 7.642 grams of the 70 mol % of amidestructural unit-containing oligomer prepared in Synthesis Example 1,2.276 g of 2,2′-bis(trifluoromethyl)benzidine (TFDB), and 1.925 g ofhexamethylene diamine (HMDA) are added thereto and dissolved, and thetemperature is set to 25° C. Then, 1.425 grams of3,3′,4,4′-biphenyltetracarboxylic dianhydride (BPDA), and 10.733 gramsof 4,4′-(hexafluoroisopropylidene)diphthalic anhydride (6FDA) are addedthereto, and the mixture is stirred for 48 hours. Then, 2.29 grams ofpyridine and 8.88 grams of acetic anhydride are added thereto, and themixture is stirred for 24 hours to obtain a poly(amic acid-amide)copolymer solution, of which the solid content is 14 weight %.

After cooling the poly(amic acid-amide) solution to a temperature of 25°C., the solution is casted on a glass substrate, and dried for 40minutes on a hot plate at a temperature of 100° C. Then, the film isseparated from the glass substrate and introduced into a conventionoven, wherein the temperature is increased from the room temperature to200° C., at a heating rate of 3° C. per minutes, maintained at 200° C.for about 20 minutes, and slowly cooled to room temperature to obtain apoly(amide-imide) copolymer film.

Example 3

136 grams of N,N-dimethyl acetamide (DMAc) as a solvent is charged intoa 4-neck double-walled 250 mL reactor equipped with a mechanical stirrerand a nitrogen inlet, while passing nitrogen gas through, and thetemperature is set to 25° C. Then, 7.921 grams of the 70 mol % of amidestructural unit-containing oligomer prepared in Synthesis Example 1,0.982 g of 2,2′-bis(trifluoromethyl)benzidine (TFDB), and 2.495 g ofhexamethylene diamine (HMDA) are added thereto and dissolved, and thetemperature is set to 25° C. Then, 1.477 grams of3,3′,4,4′-biphenyltetracarboxylic dianhydride (BPDA), and 11.125 gramsof 4,4′-(hexafluoroisopropylidene)diphthalic anhydride (6FDA) are addedthereto, and the mixture is stirred for 48 hours. Then, 2.38 grams ofpyridine and 9.21 grams of acetic anhydride are added thereto, and themixture is stirred for 24 hours to obtain a poly(amic acid-amide)copolymer solution, of which the solid content is 14 weight %.

After cooling the poly(amic acid-amide) solution to a temperature of 25°C., the solution is casted on a glass substrate, and dried for 40minutes on a hot plate at a temperature of 100° C. Then, the film isseparated from the glass substrate and introduced into a conventionoven, wherein the temperature is increased from the room temperature to200° C., at a heating rate of 3° C. per minutes, maintained at 200° C.for about 20 minutes, and slowly cooled to room temperature to obtain apoly(amide-imide) copolymer film.

Example 4

152 grams of N,N-dimethyl acetamide (DMAc) as a solvent is charged intoa 4-neck double-walled 250 mL reactor equipped with a mechanical stirrerand a nitrogen inlet, while passing nitrogen gas through, and thetemperature is set to 25° C. Then, 20.203 grams of the 70 mol % of amidestructural unit-containing oligomer prepared in Synthesis Example 1, and6.293 g of hexamethylene diamine (HMDA) are added thereto and dissolved,and the temperature is set to 25° C. Then, 17.176 grams of3,3′,4,4′-biphenyltetracarboxylic dianhydride (BPDA), and 14.3 grams of4,4′-(hexafluoroisopropylidene)diphthalic anhydride (6FDA) are addedthereto, and the mixture is stirred for 48 hours. Then, 5.39 grams ofpyridine and 20.86 grams of acetic anhydride are added thereto, and themixture is stirred for 24 hours to obtain a poly(amic acid-amide)copolymer solution, of which the solid content is 11.2 weight %.

After cooling the poly(amic acid-amide) solution to a temperature of 25°C., the solution is casted on a glass substrate, and dried for 40minutes on a hot plate at a temperature of 100° C. Then, the film isseparated from the glass substrate and introduced into a conventionoven, wherein the temperature is increased from the room temperature to200° C., at a heating rate of 3° C. per minutes, maintained at 200° C.for about 20 minutes, and slowly cooled to room temperature to obtain apoly(amide-imide) copolymer film.

Example 5

120 grams of N,N-dimethyl acetamide (DMAc) as a solvent is charged intoa 4-neck double-walled 250 mL reactor equipped with a mechanical stirrerand a nitrogen inlet, while passing nitrogen gas through, and thetemperature is set to 25° C. Then, 7.930 grams of the 70 mol % of amidestructural unit-containing oligomer prepared in Synthesis Example 1,4.735 g of 2,2′-bis(trifluoromethyl)benzidine (TFDB), and 4.007 g ofhexamethylene diamine (HMDA) are added thereto and dissolved, and thetemperature is set to 25° C. Then, 2.321 grams of3,3′,4,4′-biphenyltetracarboxylic dianhydride (BPDA), and 21.006 gramsof 4,4′-(hexafluoroisopropylidene)diphthalic anhydride (6FDA) are addedthereto, and the mixture is stirred for 48 hours. Then, 4.36 grams ofpyridine and 16.90 grams of acetic anhydride are added thereto, and themixture is stirred for 24 hours to obtain a poly(amic acid-amide)copolymer solution, of which the solid content is 22.1 weight %.

After cooling the poly(amic acid-amide) solution to a temperature of 25°C., the solution is casted on a glass substrate, and dried for 40minutes on a hot plate at a temperature of 100° C. Then, the film isseparated from the glass substrate and introduced into a conventionoven, wherein the temperature is increased from the room temperature to200° C., at a heating rate of 3° C. per minutes, maintained at 200° C.for about 20 minutes, and slowly cooled to room temperature to obtain apoly(amide-imide) copolymer film.

Example 6

120 grams of N,N-dimethyl acetamide (DMAc) as a solvent is charged intoa 4-neck double-walled 250 mL reactor equipped with a mechanical stirrerand a nitrogen inlet, while passing nitrogen gas through, and thetemperature is set to 25° C. Then, 10.681 grams of the 70 mol % of amidestructural unit-containing oligomer prepared in Synthesis Example 1,0.427 g of 2,2′-bis(trifluoromethyl)benzidine (TFDB), and 5.383 g ofhexamethylene diamine (HMDA) are added thereto and dissolved, and thetemperature is set to 25° C. Then, 2.340 grams of3,3′,4,4′-biphenyltetracarboxylic dianhydride (BPDA), and 21.17 grams of4,4′-(hexafluoroisopropylidene)diphthalic anhydride (6FDA) are addedthereto, and the mixture is stirred for 48 hours. Then, 4.40 grams ofpyridine and 17.03 grams of acetic anhydride are added thereto, and themixture is stirred for 24 hours to obtain a poly(amic acid-amide)copolymer solution, of which the solid content is 22 weight %.

After cooling the poly(amic acid-amide) solution to a temperature of 25°C., the solution is casted on a glass substrate, and dried for 40minutes on a hot plate at a temperature of 100° C. Then, the film isseparated from the glass substrate and introduced into a conventionoven, wherein the temperature is increased from the room temperature to200° C., at a heating rate of 3° C. per minutes, maintained at 200° C.for about 20 minutes, and slowly cooled to room temperature to obtain apoly(amide-imide) copolymer film.

Example 7

154 grams of N,N-dimethyl acetamide (DMAc) as a solvent is charged intoa 4-neck double-walled 250 mL reactor equipped with a mechanical stirrerand a nitrogen inlet, while passing nitrogen gas through, and thetemperature is set to 25° C. Then, 10.550 grams of the 70 mol % of amidestructural unit-containing oligomer prepared in Synthesis Example 1, and7.784 g of hexamethylene diamine (HMDA) are added thereto and dissolved,and the temperature is set to 25° C. Then, 2.737 grams of3,3′,4,4′-biphenyltetracarboxylic dianhydride (BPDA), and 28.929 gramsof 4,4′-(hexafluoroisopropylidene)diphthalic anhydride (6FDA) are addedthereto, and the mixture is stirred for 48 hours. Then, 2.35 grams ofpyridine and 18.24 grams of acetic anhydride are added thereto, and themixture is stirred for 24 hours to obtain a poly(amic acid-amide)copolymer solution, of which the solid content is 20.4 weight %.

After cooling the poly(amic acid-amide) solution to a temperature of 25°C., the solution is casted on a glass substrate, and dried for 40minutes on a hot plate at a temperature of 100° C. Then, the film isseparated from the glass substrate and introduced into a conventionoven, wherein the temperature is increased from the room temperature to200° C., at a heating rate of 3° C. per minutes, maintained at 200° C.for about 20 minutes, and slowly cooled to room temperature to obtain apoly(amide-imide) copolymer film.

Example 8

120 grams of N,N-dimethyl acetamide (DMAc) as a solvent is charged intoa 4-neck double-walled 250 mL reactor equipped with a mechanical stirrerand a nitrogen inlet, while passing nitrogen gas through, and thetemperature is set to 25° C. Then, 5.982 grams of the 70 mol % of amidestructural unit-containing oligomer prepared in Synthesis Example 1,1.882 g of 2,2′-bis(trifluoromethyl)benzidine (TFDB), and 5.987 g ofhexamethylene diamine (HMDA) are added thereto and dissolved, and thetemperature is set to 25° C. Then, 2.602 grams of3,3′,4,4′-biphenyltetracarboxylic dianhydride (BPDA), and 23.547 gramsof 4,4′-(hexafluoroisopropylidene)diphthalic anhydride (6FDA) are addedthereto, and the mixture is stirred for 48 hours. Then, 4.86 grams ofpyridine and 18.94 grams of acetic anhydride are added thereto, and themixture is stirred for 24 hours to obtain a poly(amic acid-amide)copolymer solution, of which the solid content is 21.8 weight %.

After cooling the poly(amic acid-amide) solution to a temperature of 25°C., the solution is casted on a glass substrate, and dried for 40minutes on a hot plate at a temperature of 100° C. Then, the film isseparated from the glass substrate and introduced into a conventionoven, wherein the temperature is increased from the room temperature to200° C., at a heating rate of 3° C. per minutes, maintained at 200° C.for about 20 minutes, and slowly cooled to room temperature to obtain apoly(amide-imide) copolymer film.

Comparative Example 1

152 grams of N,N-dimethyl acetamide (DMAc) as a solvent is charged intoa 4-neck double-walled 250 mL reactor equipped with a mechanical stirrerand a nitrogen inlet, while passing nitrogen gas through, and thetemperature is set to 25° C. Then, 13.446 grams of the 70 mol % of amidestructural unit-containing oligomer prepared in Synthesis Example 1, and13.199 g of 2,2′-bis(trifluoromethyl)benzidine (TFDB) are added theretoand dissolved, and the temperature is set to 25° C. Then, 2.125 grams of3,3′,4,4′-biphenyltetracarboxylic dianhydride (BPDA), and 19.230 gramsof 4,4′-(hexafluoroisopropylidene)diphthalic anhydride (6FDA) are addedthereto, and the mixture is stirred for 48 hours. Then, 4.0 grams ofpyridine and 15.47 grams of acetic anhydride are added thereto, and themixture is stirred for 24 hours to obtain a poly(amic acid-amide)copolymer solution, of which the solid content is 14 weight %.

After cooling the poly(amic acid-amide) solution to a temperature of 25°C., the solution is casted on a glass substrate, and dried for 40minutes on a hot plate at a temperature of 100° C. Then, the film isseparated from the glass substrate and introduced into a furnace,wherein the temperature is increased from the room temperature to 200°C., at a heating rate of 3° C. per minutes, maintained at 200° C. forabout 20 minutes, and slowly cooled to room temperature to obtain apoly(amide-imide) copolymer film.

Example 9

168 grams of N,N-dimethyl acetamide (DMAc) as a solvent is charged intoa 4-neck double-walled 250 mL reactor equipped with a mechanical stirrerand a nitrogen inlet, while passing nitrogen gas through, and thetemperature is set to 25° C. Then, 15.477 grams of the 70 mol % of amidestructural unit-containing oligomer prepared in Synthesis Example 1,12.660 g of 2,2′-bis(trifluoromethyl)benzidine (TFDB), and 0.976 g ofhexamethylene diamine (HMDA) are added thereto and dissolved, and thetemperature is set to 25° C. Then, 2.886 grams of3,3′,4,4′-biphenyltetracarboxylic dianhydride (BPDA), and 21.738 gramsof 4,4′-(hexafluoroisopropylidene)diphthalic anhydride (6FDA) are addedthereto, and the mixture is stirred for 48 hours. Then, 4.65 grams ofpyridine and 17.99 grams of acetic anhydride are added thereto, and themixture is stirred for 24 hours to obtain a poly(amic acid-amide)copolymer solution, of which the solid content is 11.3 weight %.

After cooling the poly(amic acid-amide) solution to a temperature of 25°C., the solution is casted on a glass substrate, and dried for 40minutes on a hot plate at a temperature of 100° C. Then, the film isseparated from the glass substrate and introduced into a furnace,wherein the temperature is increased from the room temperature to 200°C., at a heating rate of 3° C. per minutes, maintained at 200° C. forabout 20 minutes, and slowly cooled to room temperature to obtain apoly(amide-imide) copolymer film.

Example 10

168 grams of N,N-dimethyl acetamide (DMAc) as a solvent is charged intoa 4-neck double-walled 250 mL reactor equipped with a mechanical stirrerand a nitrogen inlet, while passing nitrogen gas through, and thetemperature is set to 25° C. Then, 16.347 grams of the 70 mol % of amidestructural unit-containing oligomer prepared in Synthesis Example 1,10.550 g of 2,2′-bis(trifluoromethyl)benzidine (TFDB), and 2.055 g ofhexamethylene diamine (HMDA) are added thereto and dissolved, and thetemperature is set to 25° C. Then, 3.048 grams of3,3′,4,4′-biphenyltetracarboxylic dianhydride (BPDA), and 22.959 gramsof 4,4′-(hexafluoroisopropylidene)diphthalic anhydride (6FDA) are addedthereto, and the mixture is stirred for 48 hours. Then, 4.91 grams ofpyridine and 19.0 grams of acetic anhydride are added thereto, and themixture is stirred for 24 hours to obtain a poly(amic acid-amide)copolymer solution, of which the solid content is 11.3 weight %.

After cooling the poly(amic acid-amide) solution to a temperature of 25°C., the solution is casted on a glass substrate, and dried for 40minutes on a hot plate at a temperature of 100° C. Then, the film isseparated from the glass substrate and introduced into a furnace,wherein the temperature is increased from the room temperature to 200°C., at a heating rate of 3° C. per minutes, maintained at 200° C. forabout 20 minutes, and slowly cooled to room temperature to obtain apoly(amide-imide) copolymer film.

Example 11

150 grams of N,N-dimethyl acetamide (DMAc) as a solvent is charged intoa 4-neck double-walled 250 mL reactor equipped with a mechanical stirrerand a nitrogen inlet, while passing nitrogen gas through, and thetemperature is set to 25° C. Then, 11.514 grams of the 70 mol % of amidestructural unit-containing oligomer prepared in Synthesis Example 1, and8.495 g of hexamethylene diamine (HMDA) are added thereto and dissolved,and the temperature is set to 25° C. Then, 11.949 grams of3,3′,4,4′-biphenyltetracarboxylic dianhydride (BPDA), and 18.042 gramsof 4,4′-(hexafluoroisopropylidene)diphthalic anhydride (6FDA) are addedthereto, and the mixture is stirred for 48 hour. Then, 2.57 grams ofpyridine and 19.90 grams of acetic anhydride are added thereto, and themixture is stirred for 24 hours to obtain a poly(amic acid-amide)copolymer solution, of which the solid content is 22.5 weight %.

The obtained poly(amide-imide) copolymer solution becomes gelated astime goes on, and it is not possible to fabricate a film using thesolution as whitening occurs.

Example 12

146 grams of N,N-dimethyl acetamide (DMAc) as a solvent is charged intoa 4-neck double-walled 250 mL reactor equipped with a mechanical stirrerand a nitrogen inlet, while passing nitrogen gas through, and thetemperature is set to 25° C. Then, 13.517 grams of the 70 mol % of amidestructural unit-containing oligomer prepared in Synthesis Example 1, and9.248 g of hexamethylene diamine (HMDA) are added thereto and dissolved,and the temperature is set to 25° C. Then, 16.388 grams of3,3′,4,4′-biphenyltetracarboxylic dianhydride (BPDA), and 14.846 gramsof 4,4′-(hexafluoroisopropylidene)diphthalic anhydride (6FDA) are addedthereto, and the mixture is stirred for 48 hours. Then, 2.82 grams ofpyridine and 21.84 grams of acetic anhydride are added thereto, and themixture is stirred for 24 hours to obtain a poly(amic acid-amide)copolymer solution, of which the solid content is 24 weight %.

The obtained poly(amide-imide) copolymer solution becomes gelated astime goes on, and it is not possible to fabricate a film using thesolution as whitening occurs.

Evaluation: Evaluation of the Films

Each of the poly(amide-imide) copolymer films prepared in Examples 1 to10 and Comparative Example 1 are evaluated for the composition,thickness, glass transition temperature, amount of remaining solvent,optical properties, and mechanical properties, and the obtained valuesare described in Table 1 below.

As for the optical properties, light transmittance in a wavelength rangebetween 350 nanometers (nm) to 750 nm, YI, YI difference after exposureUV ray, and haze are measured.

As for the mechanical properties, toughness and tensile modulus aremeasured.

Thickness of film is determined by using Micrometer (Mitutoyo Com.Ltd.).

Glass transition temperature (T_(g)) is measured according to ASTM D3418method by using DMA (Dynamic Mechanical Analyzer) Q800 apparatus.

An amount of solvent remained in a film is determined by using TGA(Thermogravimetric Analyzer) Q500, and by taking the decrease in weightin the region between 150° C. and 370° C. as the amount of solventremained in a film.

Yellowness index (YI), light transmittance (at a wavelength range of 350nm to 750 nm), and haze are measured for a film having a thickness ofabout 50 micrometers, according to an ASTM D1925 method by using aspectrophotometer, CM-3600d made by Konica Minolta Inc. YI difference(ΔYI) after and before exposure to UV light is measured as the YIdifference after and before exposure to an ultraviolet (UV) lamp of aUVB wavelength region for 72 hours.

Tensile modulus is measured for a sample of a film having a width of 10millimeters (mm) and a length of 50 mm by elongating each sample at arate of 0.5 mm/minute at the room temperature five times, according toASTM D882 method by using Instron 3365 apparatus.

Toughness is measured according to an ASTM D882 method, and isdetermined by calculating the total area by multiplying the X axis forstrain and the Y axis for stress.

TABLE 1 Tensile thickness Tg Solvent Haze modulus Toughness Composition[μm] [° C.] remained [%] Tr [%] (%) YI ΔYI [GPa] [Joule · m⁻³ · 10⁴]Comparative TPCl/6FDA/BPDA/TFDB = 52 353.5 3 89.8 0.2 1.66 0.76 4.3550.7 Example 1 30/60/10/100 Example 9 TPCl/6FDA/BPDA/TFDB/ 48 323.3 2.889.8 0.2 1.59 0.66 4.7 669.4 HMDA = 30/60/10/90/10 Example 10TPCl/6FDA/BPDA/TFDB/ 46 292.9 2.4 89.8 0.1 1.54 0.50 4.6 870.2 HMDA =30/60/10/80/20 Example 1 TPCl/6FDA/BPDA/TFDB/ 50 267.9 1.8 89.6 0.3 1.560.57 4.7 1498.2 HMDA = 30/60/10/70/30 Example 2 TPCl/6FDA/BPDA/TFDB/ 49250.5 1.6 89.7 0.7 1.50 0.43 4.5 1658.3 HMDA = 30/60/10/60/40 Example 3TPCl/6FDA/BPDA/TFDB/ 44 227.3 1.3 89.9 0.4 1.39 0.45 4.2 1862.6 HMDA =30/60/10/50/50 Example 4 TPCl/6FDA/BPDA/TFDB/ 52 223.2 1.3 89.9 0.3 1.590.65 4.1 1876.3 HMDA = 30/60/10/43/57 Example 5 TPCl/6FDA/BPDA/TFDB/ 55231.7 1.2 89.8 0.5 1.56 0.72 4.1 1858.4 HMDA = 20/70/10/50/50 Example 6TPCl/6FDA/BPDA/TFDB/ 55 206.1 0.9 89.9 0.4 1.58 0.54 3.8 1923.6 HMDA =20/70/10/30/70 Example 7 TPCl/6FDA/BPDA/TFDB/ 55 189.1 0.7 90.3 0.3 1.551.03 3.5 1950.4 HMDA = 20/70/10/28/72 Example 8 TPCl/6FDA/BPDA/TFDB/ 55178.1 0.6 89.8 0.5 1.53 0.92 3.4 2200.4 HMDA = 10/80/10/20/80

As shown in Table 1, the films prepared by including the linearaliphatic diamine, HMDA (hexamethylene diamine) in an amount from 30 mol% to 80 mol % according to Examples 1 to 8 have increased tensilemoduli, and moreover, increased toughness by more than 2 times, comparedwith the film according to Comparative Example 1, which is prepared bynot including the linear aliphatic diamine. Meanwhile, when comparedwith the films according to Examples 9 and 10, which are prepared byincluding less than or equal to 20 mol % of HMDA, the films according toExamples 1 to 8 show hardly changed tensile moduli or a slightlydecreased tensile moduli, while greatly increased toughness.

Further, while the film according to Comparative Example 1, which doesnot included HMDA, has a T_(g) of greater than 350° C., the filmaccording to Example 1, which includes HMDA in an amount of 30 mol %,has a T_(g) of 267.9° C., the T_(g) decreases as much as about 100° C.As the amount of HMDA increases as in Examples 2 to 10, toughnessincreases and T_(g) decreases. As T_(g) of the films according toExamples 1 to 10 decreases, the amount of solvent remained in the filmsdecreases. While the amount of solvent of the film according toComparative Example 1, which does not include HMDA, is 3%, the filmaccording to Example 1 that includes HMDA in an amount of 30 mol % has1.8% of the solvent remained in the film. That is, as the amount of HMDAincreases, the amount of solvent remained decreases by less than a half.

Meanwhile, as described above, the films according to Examples 1 to 10maintain good optical properties, while having improved mechanicalproperties, such as, for example, toughness. The films according toExamples 1 to 10 have transmittance of greater than or equal to 89%,which is equivalent or in some cases (Examples 3, 4, 6, and 7) superiorto the films according to Comparative Example 1, which does not includeHMDA. YI is also maintained as the films according to Examples 1 to 10have a YI less than or equivalent to the YI value of the film accordingto Comparative Example 1. YI difference (ΔYI) and haze of the filmsaccording to Examples 1 to 10 are also maintained compared with thataccording to Comparative Example 1.

As a result, the poly(amide-imide) copolymer prepared by including alinear aliphatic diamine along with an aromatic diamine has improvedmechanical properties, such as, for example, a toughness, whilemaintaining good optical properties, as well as having a lowered T_(g)to decrease a process temperature for fabricating a film. Further, thepoly(amide-imide) copolymer film according to an embodiment that has alowered T_(g) has decreased solvent remained in the film due to thelowered T_(g).

As described above, the poly(amide-imide) copolymer according to anembodiment prepared by reacting an aromatic diamine, an aromatictetracarboxylic dianhydride, and an aromatic dicarbonyl compound, aswell as a linear aliphatic diamine, has improved mechanical properties,such as, for example, a toughness, while maintaining good opticalproperties, and has a lowered T_(g) to reduce a process temperature,which leads to the cost reduction, as well as reduction of the amount ofsolvent remained in the final article prepared from thepoly(amide-imide) copolymer to have a more improved quality.Accordingly, the article having good optical and mechanical propertiesmay be advantageous for use in a display device, such as, for example, aflexible display device.

While this disclosure has been described in connection with what ispresently considered to be practical exemplary embodiments, it is to beunderstood that the present disclosure is not limited to the embodimentspresented herein, but on the contrary, is intended to cover variousmodifications and equivalent arrangements included within the spirit andscope of the appended claims.

1.-20. (canceled)
 21. A composition for preparing a poly(amide-imide)copolymer comprising a substituted or unsubstituted linear aliphaticdiamine, a compound represented by Chemical Formula 4, and atetracarboxylic acid dianhydride represented by Chemical Formula 3:

wherein, in Chemical Formula 4, R³ is a substituted or unsubstitutedphenylene or a substituted or unsubstituted biphenylene group, n0 is anumber greater than or equal to 1, and Ar¹ and Ar² are eachindependently represented by Chemical Formula 5:

wherein, in Chemical Formula 5, R⁶ and R⁷ are each independently anelectron withdrawing group selected from —CF₃, —CCl₃, —CBr₃, —Cl₃, —NO₂,—CN, —C(═O)CH3, and —CO₂C₂H₅, R⁸ and R⁹ are each independently ahalogen, a hydroxy group, a substituted or unsubstituted C1 to C10aliphatic organic group, a substituted or unsubstituted C6 to C20aromatic organic group, an alkoxy group of formula —OR²⁰⁴, wherein R²⁰⁴is a C1 to C10 aliphatic organic group, or a silyl group of formula—SiR²⁰⁵R²⁰⁶R²⁰⁷ wherein R²⁰⁵, R²⁰⁶, and R²⁰⁷ are each independentlyhydrogen or a C1 to C10 aliphatic organic group, n3 is an integerranging from 1 to 4, n5 is an integer ranging from 0 to 3, provided thatn3+n5 is an integer ranging from 1 to 4, and n4 is an integer rangingfrom 1 to 4, n6 is an integer ranging from 0 to 3, provided that n4+n6is an integer ranging from 1 to 4;

wherein, in Chemical Formula 3, R¹⁰ is a single bond, —O—, —S—, —C(═O)—,—CH(OH)—, —C(═O)NH—, —S(═O)₂—, —Si(CH₃)₂—, —(CH₂)_(p)—, —(CF₂)_(q)—,—C(C_(n)H_(2n+1))₂—, —C(C_(n)F_(2n+1))₂—,—(CH₂)_(p)C(C_(n)H_(2n+1))₂(CH₂)_(q)—, or—(CH₂)_(p)C(C_(n)F_(2n+1))₂(CH₂)_(q)— wherein 1≤n≤10, 1≤p≤10, and1≤q≤10, R¹² and R¹³ are each independently a halogen, a hydroxy group, asubstituted or unsubstituted C1 to C10 aliphatic organic group, asubstituted or unsubstituted C6 to C20 aromatic organic group, an alkoxygroup of formula —OR²⁰¹, wherein R²⁰¹ is a C1 to C10 aliphatic organicgroup, or a silyl group of formula —SiR²¹⁰R²¹¹R²¹², wherein R²¹⁰, R²¹¹,and R²¹² are each independently hydrogen or a C1 to C10 aliphaticorganic group, and n7 and n8 are each independently an integer rangingfrom 0 to
 3. 22. The composition for preparing a poly(amide-imide)copolymer according to claim 21, wherein the substituted orunsubstituted linear aliphatic diamine comprises two terminals, whereinthe substituted or unsubstituted linear aliphatic diamine comprises anamino group located at each end of the two terminals thereof, andwherein the substituted or unsubstituted linear aliphatic diamine is asubstituted or unsubstituted C1 to C30 saturated or unsaturated linearaliphatic diamine.
 23. The composition for preparing a poly(amide-imide)copolymer according to claim 21, wherein the substituted orunsubstituted linear aliphatic diamine comprises two terminals, whereinthe substituted or unsubstituted linear aliphatic diamine comprises anamino group located at each end of the two terminals thereof, andwherein the substituted or unsubstituted linear aliphatic diamine is asubstituted or unsubstituted C1 to C20 saturated linear aliphaticdiamine.
 24. The composition for preparing a poly(amide-imide) copolymeraccording to claim 21, wherein the substituted or unsubstituted linearaliphatic diamine is selected from methylene diamine, ethylene diamine,1,3-propane diamine, 1,4-tetramethylene diamine, 1,5-pentamethylenediamine, 1,6-hexamethylene diamine, 1,7-heptamethylene diamine,1,8-octamethylene diamine, 1,9-nanomethylene diamine, 1,10-decamehtylenediamine, 1,11-undecamethylene diamine, 1,12-dodecamethylene diamine, anda combination thereof.
 25. The composition for preparing apoly(amide-imide) copolymer according to claim 21, wherein thecomposition further comprises a diamine represented by Chemical Formula1:NH₂-A-NH₂  Chemical Formula 1 wherein in Chemical Formula 1, A is a ringsystem comprising two or more C6 to C30 aromatic rings linked by asingle bond, wherein each of the two or more aromatic rings isindependently unsubstituted or substituted by an electron-withdrawinggroup.
 26. The composition for preparing a poly(amide-imide) copolymeraccording to claim 25, wherein the diamine represented by ChemicalFormula 1 comprises a ring system comprising two C6 to C12 aromaticrings linked by a single bond, wherein each of the two C6 to C12aromatic rings are independently substituted by an electron-withdrawinggroup selected from a halogen atom, a nitro group, a cyano group, a C1or C2 haloalkyl group, a C2 to C6 alkanoyl group, and a C2 to C6 estergroup.
 27. The composition for preparing a poly(amide-imide) copolymeraccording to claim 25, wherein the diamine represented by ChemicalFormula 1 comprises at least one selected from the diamines representedby chemical formulae:


28. The composition for preparing a poly(amide-imide) copolymeraccording to claim 25, wherein the diamine represented by ChemicalFormula 1 comprises a diamine represented by Chemical Formula A:


29. The composition for preparing a poly(amide-imide) copolymeraccording to claim 21, wherein in Chemical Formula 4, R³ is a phenylenegroup.
 30. The composition for preparing a poly(amide-imide) copolymeraccording to claim 21, wherein the tetracarboxylic acid dianhydriderepresented by Chemical Formula 3 comprises at least one selected from3,3′,4,4′-biphenyl tetracarboxylic dianhydride (BPDA),3,3′,4,4′-diphenylsulfone tetracarboxylic dianhydride (DSDA),4,4′-(hexafluoroisopropylidene)diphthalic anhydride (6FDA), and4,4′-oxydiphthalic anhydride (ODPA).
 31. The composition for preparing apoly(amide-imide) copolymer according to claim 21, wherein thetetracarboxylic acid dianhydride represented by Chemical Formula 3comprises a combination of the compound represented by Chemical Formula3-1, and the compound represented by Chemical Formula 3-2:


32. The composition for preparing a poly(amide-imide) copolymeraccording to claim 21, wherein the substituted or unsubstituted linearaliphatic diamine is present in an amount of greater than 20 molepercent and less than 90 mol percent based on the total amount ofdiamines present in the composition.
 33. An article comprising apoly(amide-imide) copolymer prepared from the composition according toclaim
 21. 34. The article according to claim 33, wherein the articlecomprises a film, and wherein the film has a toughness of greater thanor equal to 1,000 Joules×reverse cubic meters×10⁴ (Joul·m⁻³·10⁴), whenthe film has a thickness of about 30 micrometers to about 100micrometers.
 35. A window film for a display device comprising apoly(amide-imide) copolymer prepared from the composition according toclaim
 21. 36. A display device comprising the article according to claim33.
 37. The display device according to claim 26, wherein the displaydevice comprises a flexible display device.
 38. A display devicecomprising the window film according to claim 35.